1. Field of the Invention
The techniques disclosed herein relate to zoom lens systems, lens barrels, interchangeable lens apparatuses, and camera systems. In particular, the techniques disclosed herein relate to: compact and lightweight zoom lens systems having less aberration fluctuation in association with focusing, and excellent optical performance over the entire focusing condition with sufficiently compensated aberrations particularly in a close-object in-focus condition; and lens barrels, interchangeable lens apparatuses, and camera systems, each employing the zoom lens system.
2. Description of the Background Art
In recent years, interchangeable-lens type digital camera systems (also referred to simply as “camera systems”, hereinafter) have been spreading rapidly. Such  interchangeable-lens type digital camera systems realize: capturing of high-sensitive and high-quality images; high-speed focusing and high-speed image processing after image taking; and easy replacement of an interchangeable lens apparatus in accordance with a desired scene. Meanwhile, an interchangeable lens apparatus having a zoom lens system that forms an optical image with variable magnification is popular because it allows free change of focal length without the necessity of lens replacement.
Compact zoom lens systems having excellent optical performance from a wide-angle limit to a telephoto limit have been desired as zoom lens systems to be used in interchangeable lens apparatuses. Various kinds of zoom lens systems having multiple-unit constructions, such as four-unit construction and five-unit construction, have been proposed. In such zoom lens systems, focusing is usually performed so that some lens units in a lens system are moved in a direction along the optical axis. However, when performing focusing from an infinity in-focus condition to a close-object in-focus condition by a single lens unit, since an amount of movement of this lens unit responsible for focusing is determined by the paraxial power configuration in the entire lens system, it is difficult to sufficiently compensate the amount of aberration fluctuation from a wide-angle limit to a telephoto limit.
In order to reduce aberration fluctuation in focusing, zoom lens systems are proposed, in which a plurality of lens units in each lens system are moved independently from each other in a direction along the optical axis.
Japanese Laid-Open Patent Publication No. 2009-163271 discloses a zoom lens having four-unit construction of positive, negative, positive, and positive, with its overall length being fixed. In this zoom lens, a second lens unit and a fourth lens unit independently move in focusing.
Japanese Laid-Open Patent Publication No. 2001-281522 discloses a zoom lens having four-unit construction of positive, negative, positive, and negative, with its overall length being fixed. In this zoom lens, a second lens unit, a third lens unit, and a fourth lens unit move together in focusing.
Japanese Laid-Open Patent Publication No. 02-256011 discloses a zoom lens system having four-unit construction of positive, negative, positive, and positive. In this zoom lens system, all lens units independently move in zooming, and a third lens unit and a fourth lens unit independently move in focusing.
In each of the zoom lenses disclosed in Japanese Laid-Open Patent Publications Nos. 2009-163271 and 2001-281522, and in the zoom lens system disclosed in Japanese Laid-Open Patent Publication No. 02-256011, although aberration fluctuation in focusing is reduced to some extent, compensation of various aberrations particularly in a close-object in-focus condition is insufficient. Therefore, none of these zoom lenses and zoom lens system has excellent optical performance over the entire object distance from an infinite object distance to a close object distance, and is sufficiently compact.